Background: Bruises are the most common injury found among victims of violence. Forensic nurses and other health professionals are often asked to assess these injuries and determine if they are consistent in age with a given history by the patient, caregiver, or accused perpetrator. Research on determining bruise age by color using the naked eye is sparse and relies on subjective interpretation of color. Colorimetry (CIE — L*a*b*) provides a more objective alternative, but the reliability of this technology on bruises has not been formally tested. Current literature on measuring the change in bruise colorimetry over time has been limited to primarily small, descriptive studies with homogeneous samples and no studies have examined the effect of skin color, sex, and subcutaneous fat on the change in bruise color over time.

Objectives: In a population of healthy adult men and women, this study aimed to: a) determine the test-retest and inter-rater reliability of the Minolta^® Chroma-meter CR-400 in measuring bruise colorimetry of inflicted bruises; b) determine the relationship between time and colorimetry measures of bruises during the first four days after bruise creation; c) determine if skin color, sex, subcutaneous fat are predictors of the bruise colorimetry measures during this period of time; and d) determine if sex and subcutaneous fat moderate the relationship between time and bruise colorimetry.

Design and Methods: This study used a prospective, predictive, correlational design in which bruises were created under the controlled application of a paintball pellet. The subsequent bruise was measured daily for four days. Intraclass correlation coefficients were used to analyze the reliability of the instrument, while General Linear Mixed Modeling examined the change in bruise colorimetry over time and the relationship of the other independent variables on that change.

Sample: Quota sampling was employed to obtain a convenience sample of 103 healthy, adult volunteers with nearly equal representation of both sexes (51% female) and individuals of light (33%), medium (34%), and dark (33%) skin colors from the Johns Hopkins University community.

Findings: The Minolta^® Chroma-meter CR-400 demonstrated high test-retest and inter-rater reliability and precision in its measurements of bruise color (ICC = 0.966 − 0.999). The change in bruise colorimetry over four days was significant for all three color parameters (L*a*b*), with a notable change per hour for a* of -0.016 (95%Cl: -0.021, -0.012) and b* of 0.0099 (95%Cl: 0.0048, 0.015) starting at 24 hours. When compared to individuals with dark skin color, those with light skin had lighter bruises (β = 6.8; 95%Cl: 2.8, 10.8) and those with medium skin color had bruises that redder bruises (β = 0.79; 95%Cl: 0.143, 1.4). Sex and subcutaneous fat were not significant predictors. The size of the bruise was both a significant predictor and moderator and may have accounted for the effect of sex or subcutaneous fat.

Conclusion: This study has demonstrated the ability to model the change in bruise colorimetry over time on a diverse sample of healthy adults. This study has demonstrated that multiple factors, including skin color and the size of the bruise, must be considered when examining bruise color in relation to its age.